Homeostasis and negative feedback Starter Remembering back to

Homeostasis and negative feedback

Starter Remembering back to GCSE what does the term homeostasis mean? �Homeostasis literally means "same state" and it refers to the process of keeping the internal body environment in a steady state. �The importance of this cannot be over-stressed, and a great deal of the hormone system and autonomic nervous system is dedicated to homeostasis.

Homeostasis Learning objectives Success criteria �Developing your understanding of homeostasis and feedback mechanisms �Define the terms homeostasis, negative feedback and positive feed back �Explain the principles of homeostasis in terms of receptors, effectors and negative feedback;

Homeostasis �From the textbook p 6 write a definition of homeostasis �Homeostasis involves maintenance of the internal environment in a constant state despite external changes. Examples include: �Blood p. H �Blood carbon dioxide levels �Blood glucose concentration �Body temperature �Blood pressure �Water balance

Negative feedback �All homeostatic mechanisms use negative feedback to maintain a constant value. �Negative feedback means that whenever a change occurs in a system, the change automatically causes a corrective mechanism to start, which reverses the original change and brings the system back to normal. �It also means that the bigger then change the bigger the corrective mechanism.

Negative feedback �So in a system controlled by negative feedback the level is never maintained perfectly, but constantly oscillates about the set point. An efficient homeostatic system minimises the size of the oscillations. �Minor changes may not cause a response.

Negative feedback loop Stimulus Receptor Communication pathway Effector Response

Positive feedback �Less common �Response is to increase the original change Effector reacts to increase change

Task �Complete the worksheet (p 28 of green book)

�Enzyme Action and Temperature Regulation �As core body temperature rises the increase will affect the activity of enzymes. This can lead to heat exhaustion and even death �Describe the effect of increasing temperature on enzyme action �Suggest what actually causes death as the body temperature rises